1. Field of the Invention
Exemplary embodiments of the present invention generally relate to an image forming apparatus that can effectively use a drive unit for image forming.
2. Discussion of the Related Art
A four-drum-type image forming apparatus, also called a tandem-type electrophotographic image forming apparatus, is expected to meet recent demands for an increase in print speed and image quality of color image forming apparatuses and is increasing its share of the market therefor.
In one known tandem-type electrophotographic image forming apparatus, four image forming units form single color toner images different from each other on respective surfaces of image bearing members provided therein, and the single color toner images are sequentially transferred either directly onto a transfer sheet carried by a sheet conveyor belt or onto an image transfer belt before the transfer sheet so as to form a composite, full-color toner image fast. In an effort to effectively increase both the print speed and the image quality further, attention has focused on an intermediate transfer unit as a transfer unit of the tandem-type electrophotographic image forming apparatus.
However, a related problem is that the tandem-type electrophotographic image forming apparatus can cause improper composition of the single color images resulting in color shift in a composite image, thereby degrading the quality of the composite image.
One approach to solve this problem is to provide a so-called “color shift correction” that can eliminate the drawback by forming toner pattern images on a transfer belt, causing an optical sensor to detect the toner pattern images, and adjusting a timing of optical writing based on the information detected by the optical sensor. Further, a shutter controlled by a solenoid, for example, is provided to cover the optical sensor unit and open only when detecting toner pattern images, so as to protect the optical sensor unit from contamination due to toner particles scattered inside the image forming apparatus, which degrades detection accuracy of the optical sensor.
However, it is likely that toner pattern images formed on the image transfer belt during such color shift correction adhere to and contaminate a secondary transfer roller that is held in contact with the image transfer belt used in the intermediate transfer unit, and therefore a back side of the transfer sheet is also contaminated.
To prevent such contamination of the back side of the transfer sheet, another known image forming apparatus further employs a mechanism to switch a position of the secondary transfer roller, i.e., to periodically contact and separate from the image transfer belt, so that the secondary transfer roller can separate from the image transfer belt during the color shift correction. Further, in such image forming apparatus the shutter is provided to prevent the detection accuracy of the optical sensor from deteriorating, a fixed motor is used as a drive source, a solenoid is provided in a drive array and disposed near the shutter, and a swing mechanism is also provided in the drive array and disposed near the fixing motor. By controlling forward and reverse rotations of the fixed motor, this configuration opens and closes the shutter and controls the contact and separation of the secondary transfer roller.
The above-described configuration, however, requires additional mechatronics parts and components such as solenoid and brush motor, which can cause an increase in cost, power consumption, and machine size. Moreover, the additional mechatronics parts and components can adversely affect the reliability of the image forming apparatus.
Therefore, there is still a need for an image forming apparatus that can effectively operate (open and close) the shutter and control the movement of the secondary transfer roller without adding mechatronics parts and components and increasing machine size, costs, and power consumption.